1. Field of the Invention
The present general inventive concept relates to an image forming apparatus, and more particularly, to a duplex image forming apparatus which is capable of printing both surfaces of a printing medium, e.g., paper.
2. Description of the Related Art
An image forming apparatus is an apparatus that prints an image on a printing medium, e.g., paper, according to an inputted image signal. An image forming apparatus is classified as a simplex image forming apparatus which prints only one surface (front surface) of paper, or a duplex image forming apparatus which also prints a rear surface of paper by reversing the paper after printing a front surface.
The duplex image forming apparatus generally includes a paper supplying part to supply the paper, an image forming part to form an image on the supplied paper, and a paper discharge part to discharge the printed paper having passed through the image forming part to the outside.
The duplex image forming apparatus further includes a duplex printing part which is provided with duplex rollers so as to feed again the paper, whose front surface has been printed, to the image forming part to print a rear surface of the paper.
The duplex printing part rotates the duplex rollers to feed again the paper, which is fed by the reverse rotation of discharge rollers provided in the paper discharge part, to the image forming part. Accordingly, the paper whose front surface has been printed is fed again to the image forming part via a duplex print path, and the rear surface of the paper is printed.
The duplex rollers have a function of registering the paper fed by the duplex rollers, as well as reversely feeding the paper whose front surface has been printed.
However, because a portion of the paper fed by the duplex rollers is also caught in the discharge rollers, it is not easy for the duplex rollers to register to the paper by the discharge rollers.
For instance, the conventional duplex image forming apparatus includes center-feed type discharge rollers which are disposed at positions corresponding to a center portion of the paper, and side-feed type duplex rollers which are disposed at positions corresponding to sides of the paper. The duplex rollers are typically set to register the paper at the positions corresponding to the sides of letter paper.
Because the duplex rollers register the paper at the positions corresponding to the sides of the letter paper, in order to register the A4 paper, the paper should be shifted by a predetermined distance, e.g., 3 mm or more, in a transverse direction of the paper. However, because an end portion of the paper which is registered by the duplex rollers is caught in the discharge rollers, it is difficult to register the paper.